Electrical Grounding and Corrosion

[bim802000]

Hi,

There have been some debate regarding the routing of bare copper conductor in with the steel underground water pipes (in contact with each each other).

The construction team wanted to do it to save time and cost in excavation works, while the design engineers doesn't want to because of the effects of galvanic reactions. Here's the recommendation from the design engineers:

To qoute:

"Routing the ground grid in parallel with the fire water line is not recommended due to the following reasons:
a) Galvanic reaction between dissimilar metals: Two different metals should never be routed in contact with each other. The metal which is less ?noble? (in this case the fire water pipe) will corrode easily. This is especially true during rainy season in the Philippines where the soil will be usually wet. The wet soil acts as an electrolyte for the fire water pipes and ground grid copper wires.
b) Ground grids will contain stray currents since they are expected to carry line-to-ground faults and, thus, hastening the effect of the galvanic reaction.
c) Fire water pipes are considered to be critical for safety and cannot be subjected to the effects of galvanic corrosion.
Please refer to the attached excerpt from paragraph 4.4.5 of IEEE 142 for the concept of galvanic reaction between two dissimilar type of metals. If routing of the fire water line and the ground grid cannot be avoided, a minimum spacing of 600mm (based on another project) should be maintained between them."

Any comment about this anyone?

 

[kwired]

I feel the pipe is already a good electrode and it is pointless to run the copper in close proximity to it.

If you want more electrode, run the copper someplace else where it will actually make more electrode.

 

[bim802000]

Kwired,

I?ll describe the scenario in detail. The setting is a petrochemical plant. We usually make a ground grid (bare copper wires) instead of using the water pipes as our main ground electrode. It so happened that there were lots of areas where many of the grids ran on one side of the road and the water pipes ran on the opposite side.

Now, there are arguments on whether or not to route the copper wires on the same trench with the water pipes. Construction team wants to route these on the same trench, with the copper wire touching the surface of the pipe while Design team, argues that there should be a minimum spacing between them to avoid the galvanic reaction.


********************
And there?s this quote in the IEEE 142 about the subject which contradicts some other reference in this forum (http://forums.mikeholt.com/showthre...pe-corrosion-from-electri?highlight=corrosion). The thread said that the reference came from AWWA.

I?d like to know if there really is a contradiction or I may be missing something here.

 

[kingpb]

Underground piping, particularly carbon steel, stainless steel, or copper piping needs to maintain at least 12'' separation from grounding conductors. This is to electrically isolate the pipe from being grounded. Also, it is important that the piping is at least 3" away from structural steel, reinforcing steel and the like, and have external non-corrosive coating.

The piping should be cathodically protected, but that is outside the scope of the OP.